This invention generally relates to tuning arrangements and tuning components for use in microwave devices, in particular for use in microwave communication devices such as microwave circulators and isolators.
Microwave devices such as microwave circulators or microwave isolators, e.g. for use in radio link systems, generally comprise closed conductive housings defining a cavity. Typically, these housings consist of two half shells made from metal and their production technique is based on milling and drilling. Microwave circulators/isolators of the kind are, for example, described in U.S. Pat. No. 6,066,992 and GB 2 320 369 A, and GB 2 354 885 A.
In the case of microwave circulators or isolators, the two metal half shells are screwed together after assembly of, for instance, a strip-line conductor, ferrites, and flange adapters, e.g. SMA flange adapters. The tolerances of the ferrites are compensated by mechanical adjustment or integration of soft sheets on the ferrite disks. In order to satisfy electromagnetic compatibility (EMC) requirements, silver loaded epoxy is used to close leakage gaps. However, in spite of this elaborate and costly construction, the EMC behavior may change over time, and the isolator tends to leak again after 1 or 2 years.
Recently, housings made from metallized plastic have been proposed (cf. E. Habinger, A. Sidhu, G. Blasek, xe2x80x9cMetallisieren von Kunststoffgehxc3xa4usen unter EMV-, Umwelt-, and Recyclingaspektenxe2x80x9d, Eugen G.Leuze Verlag, Saulgau, 1998). By the implementation of plastic technology assembly time production cost can be reduced.
Generally, a tuning arrangement is also arranged at the housing. The tuning arrangement typically comprises a rod like tuning element made from a conductive material having one portion, referred to as the tuning portion, protruding into the cavity and thereby concentrating the electromagnetic field in the region of the tuning element. Another portion of the tuning element, referred to as the locking portion, mechanically engages the housing thereby forming an electrically conductive connection with the housing. Typically, the tuning element engages the housing via a screw thread. By rotating the tuning element with respect to the housing the protrusion length of the tuning element, i.e. of the tuning portion, can be adjusted and the resonant frequency of the cavity can be controlled.
In microwave circulators or insulators, the application of tuning elements is generally necessary to compensate material parameter tolerances of magnets and ferrites. In addition, the mechanical variation of the stripline center conductor can be compensated. In this case rotating tuning elements, having a locking portion configured as a thread, provide an ideal interface for automated tuning devices described in P. Harscher, J. Hoffmann, R. Vahldieck, B. Ludwig, xe2x80x9cAutomatic computer-controlled tuning system for microwave filtersxe2x80x9d, 2000 EuMC Conference Proceedings, Paris, 2000, October, Vol.1, pp 39-42.
FIG. 1 shows a prior art tuning element 1 basically formed as a screw and acting as an adjustable shunt capacitor Ct towards the center conductor 3. The displacement current between the tuning portion 5 and the center conductor 3 generates a surface current on the locking portion 7, i.e. on the thread. In this configuration the thread has to provide a perfect electrical contact with the housing 9.
In a solid metal housing this can be obtained without problems. In housings made from metallized plastic, however, the reliability of the electrical connection presents a problem, considering difficulties related to the metallization process of threads as well as avoiding destruction of contact surfaces while pushing sockets into such metallized housings.
It is therefore an object of the invention to provide a reliable tuning arrangement which can be utilized in metal housings as well as in plastic housings of microwave devices.
In order to satisfy this and other objects, the present invention provides a tuning arrangement for influencing an electric field within a microwave device having electrically conductive walls for guiding microwaves, the arrangement comprising at least one tuning element capacitively coupled to a portion of said electrically conductive walls through a physical connection therewith, the physical connection being an electrically insulating connection.
Due to the insulating nature of the connection between the tuning element and the electrically conductive walls of the microwave device, e.g. the housing of the device, this tuning arrangement is particularly well suited for housings made from metallized plastic in which the metallization may be abraded during mounting of the tuning arrangement in the housing.
Alternatively, this tuning element is well suited for applications where passive intermodulation arises from contact problems of a screw used to connect the tuning element to the or a housing.
Preferably, the tuning element comprises, in sequence, a tuning portion for influencing the electric field, a capacitive coupling portion which couples capacitively with said portion of said electrically conductive walls, an insulating portion, and a conductive or insulating locking portion. Due to this design, particularly due to the insulating portion of the tuning element, an electrical separation of the tuning portion and the locking portion is achieved forcing the tuning portion to interact capacitively with the housing of the device.
In accordance with another aspect of the present invention, a microwave device is provided comprising electrically conductive walls for guiding microwaves and at least one tuning element protruding into a space defined by said electrically conductive walls for influencing said microwaves, said tuning element being capacitively coupled to a portion of said electrically conductive walls through a physical connection therewith, the physical connection being an electrically insulating connection.
Preferably, the electrically conductive walls are made from metallized plastic. Due to the implementation of plastic technology for microwave components, e.g. by realizing a complete housing by two metallized plastic parts, which are screwed together, and by using e.g. push-in connectors, the assembly effort and assembly time of the device of the invention can be reduced. Further, the housing may be made elastic and, thus, can properly compensate the mechanical tolerances in the ferrite region. The assembly technique and the material characteristics yield excellent EMC behavior. Moreover, for a modular radio or microwave system the same housing can be applied for a wide frequency spectrum (e.g. 5.9 GHz-13.5 GHz).
Preferably, a portion of the electrically conductive walls adjacent to ferrite disks arranged on opposite sides of a center conductor is elastic. Due to the elastic behavior of the electrically conductive walls the ferrite disks and the electrically conductive walls are pressed together. Hence, air gaps between the ferrite disks and the housing can be avoided in a simple manner. Mechanical tolerances can be compensated by this membrane-concept.
When the microwave device is realized as an isolator, an absorber element incorporated in the device is advantageously formed from an attenuating silicone material. This material is elastic and adapts to the housing geometry allowing an easy and quick integration. Minor deformations do not influence the return loss. Since the design tolerates slight deviations this silicone absorber can be produced using casting techniques. The position in the housing may be fixed using a xe2x80x9csnap-in techniquexe2x80x9d.
In accordance with still another aspect of the present invention, a tuning component is provided comprising a metal socket or an insulating socket for insertion into a space defined by electrically conductive walls and a tuning element, the tuning element comprising a conductive or insulating locking portion having a screw thread engagable with said socket, an insulating portion connected to said locking portion and a tuning portion connected to said insulating portion and remote from said locking portion.
In accordance with yet another aspect of the present invention, a method of influencing an electrical field in a microwave device having electrically conductive walls for guiding microwaves is provided, the method comprising the step of adjusting the protrusion of at least one tuning element into a space defined by said electrically conductive walls with the tuning element coupling capacitively with a portion of said electrically conductive walls.
The above objects and other objects, features, and advantages of the present invention are readily apparent from the following detailed description of a preferred mode for carrying out the invention when taken with the accompanying drawings.